An elementary cell of a Li-ion storage battery or lithium battery comprises an anode (at discharge), generally made of lithium metal or based on carbon, and a cathode (likewise at discharge), generally made of a lithium insertion compound of metal oxide type, such as LiMn2O4, LiCoO2 or LiNiO2, between which is inserted an electrolyte which conducts lithium ions.
A cathode or an anode generally comprises at least one current collector on which is deposited a composite material which consists of: one or more “active” materials, active because they exhibit an electrochemical activity with respect to lithium, one or more polymers which act as binder and which are generally functionalized or nonfunctionalized fluoropolymers, such as polyvinylidene fluoride, or aqueous-based polymers of carboxymethylcellulose type or styrene/butadiene latexes, plus one or more electron-conducting additives which are generally allotropic forms of carbon.
The conventional active materials at the negative electrode are generally lithium metal, graphite, silicon/carbon composites, silicon, fluorographites of CFx type with x between 0 and 1, and titanates of LiTi5O12 type.
The conventional active materials at the positive electrode are generally of the LiMO2 type, of the LiMPO4 type, of the Li2MPO3F type, of the Li2MSiO4 type, where M is Co, Ni, Mn, Fe or a combination of these, of the LiMn2O4 type or of the S8 type.
Recently, additives which make it possible to improve the permeability of the electrolyte to the core of the electrode have been used. As a result of the growing demand for high-energy batteries, that is to say batteries with higher electric storage capacities, the thickness of the electrodes is increasing and thus the permeability of the electrolyte is becoming important in the overall resistance of the battery. With the aim of improving this permeability, the document WO2005/011044 describes the addition of “inorganic” fillers of metal oxides, such as Al2O3 and SiO2. These inorganic fillers are added during the conventional process for the manufacture of electrodes. This conventional process consists in mixing the different constituents in a solvent or a mixture of solvents, such as, for example, N-methylpyrrolidone, acetone, water or ethylene carbonate:                1. at least one conducting additive at a content ranging from 1 to 5% by weight, preferably from 1.5 to 4% or 1 to 2.5% by weight, preferably from 1.5 to 2.2% by weight, with respect to the total weight of the composite material;        2. a lithium oxide, phosphate, fluorophosphate or silicate as electrode active material capable of reversibly forming an insertion compound with lithium, having an electrochemical potential greater than 2V with respect to the Li/Li+ pair;        3. a polymer binder.        
The ink obtained is subsequently coated onto the current collector and the solvent or solvents are evaporated by heating ranging from 30 to 200° C.
The failings of these inorganic fillers are that they decrease the amount of active material in the electrode and thus the capacity of the battery but also these fillers only make it possible to improve the macroscopic diffusion of the electrolyte.
In point of fact, in the electrode, it is the charging resistance of the active material/electrolyte interface which is limiting for the performance of the battery. This resistance is a microscopic effect which cannot be improved by the addition of macroscopic inorganic filler.
The applicant has discovered that the addition of a salt consisting of an organic anion, chosen in order to have a favorable interaction at the surface of the active material, makes it possible to increase the ionic conductivity of the electrode.
Furthermore, an improvement in the cohesion and adhesion properties of the electrode on metal by the specific choice of the polymer binder has been looked for.